The overall objective of this proposal is to systematically develop our understanding of gene regulation in virus infected cells and to use this knowledge for developing in vitro systems from which activities can be purified and characterized. The following is a list of these projects which deals with four viruses: the papova viruses SV40 and polyoma, the papovirus MVM and the retrovirus MLV. Studies with SV40 and polyoma: 1) Purification characterization and biological functions of poly(A) minus viral specific RNAs. 2) "Attenuation" as a mechanism for regulating transcription. 3) Characterization of minichromosomes of substituted SV40 DNA molecules. 4) Characterization of minichromosomes having transcriptional activities. 5) Transcriptional initiation in vitro using either E. coli polymerase or eukaryotic polymerase II and viral minichromosomes. 6) The relation of the cytoskeleton structure to mRNA biogenesis. Studies with MVM: 1) Isolation and characterization of transcriptional complexes. 2) The possibility that MVM DNA has a minichromosome structure. Studies with MLV: 1) Characterization of poly(A) plus and poly(A) minus viral RNAs.